1. Field of the Invention
The present invention relates to an image capturing apparatus and a distance measuring method for obtaining information regarding a depth-direction distance to a subject. More particularly, the present invention relates to an image capturing apparatus and a distance measuring method for obtaining the information regarding a depth of the subject by capturing outgoing light beams from the subject that is illuminated with light.
2. Description of the Related Art
As a method for obtaining information regarding a distance to an object or information regarding a position of the object, a three-dimensional image measuring method is known in which light having a pattern of, for example, a slit or a stripe, is cast onto the object and the pattern cast onto the object is captured and analyzed. There are a slit-light projection method (light cutting method) and a coded-pattern light projection method as typical measuring methods, which are described in detail in xe2x80x9cThree-dimensional image measurementxe2x80x9d by Seiji Inokuchi and Kosuke Sato (Shokodo Co., Ltd.).
Japanese Patent Application Laying-Open No. 61-155909 (published on Jul. 15, 1986) and Japanese Patent Application Laying-Open No. 63-233312 (published on Sep. 29, 1988) disclose a distance measuring apparatus and a distance measuring method in which light beams are cast onto a subject from different light-source positions and the distance to the subject is measured based on the intensity ratio of the reflected light beams from the subject.
Japanese Patent Application Laying-Open No. 62-46207 (published on Feb. 28, 1987) discloses a distance detecting apparatus that casts two light beams having different phases onto the subject and measures the distance to the subject based on the phase difference between the light beams reflected from the subject.
Moreover, xe2x80x9cDevelopment of Axi-Vision Cameraxe2x80x9d, Kawakita et al., 3D Image conference ""99, 1999, discloses a method for measuring the distance to the subject in which the subject that is illuminated with light having the intensity modulated at a very high speed is captured by a camera having a high-speed shutter function, and the distance to the subject is measured from the degree of the intensity modulation that varies depending on the distance to the subject.
Japanese Patent Application Laying-Open Nos. 10-48336 and 11-94520 disclose an actual time-range finder that calculates the distance to the subject by casting different light patterns having different wavelength characteristics onto the subject and extracting wavelength components of light reflected from the subject incident light.
In the conventional distance measuring apparatus and method, the time difference occurs in the measurement because it is necessary to successively cast the light from the different emission positions so as to measure the reflected light beams, as disclosed in Japanese Patent Applications Laying-Open Nos. 61-155909 and 63-233312. Thus, in a case of the moving subject, the distance cannot be measured. In addition, during a time period in which the position of the light source is changed to change the emission position, the measurement error may occur because of waver of the capturing apparatus.
Moreover, in a case of using light beams having different wavelength characteristics, the light beams can be emitted simultaneously, and the reflected light beams can be separated by a filter prepared in accordance with the wavelength characteristics of the light beams, so that the intensities of the reflected light beams can be measured. However, if the spectral reflectance of the subject varies depending on the wavelength, the intensities of the reflected light beams are also different depending on the wavelength thereof. The difference of the reflected-light intensities between the wavelengths may cause an error when the depth-direction distance is calculated from the ratio of the intensities of the reflected light beams, thereby preventing the precise calculation of the depth-direction distance.
The actual time-range finder disclosed in Japanese Patent Applications Laying-Open Nos. 10-48336 and 11-94520 also uses the light having different wavelength characteristics for calculating the distance to the subject. In a case where spectral reflectance is varied depending on a position of the illuminated portion of the subject, however, the error may be caused, thus preventing the precise calculation of the depth-direction distance.
The distance measuring apparatus disclosed in Japanese Patent Application Laying-Open No. 62-46207 requires a high-precision phase detector for detecting the phase difference. This makes the apparatus expensive and loses the simplicity of the apparatus. In addition, since this apparatus measures the phase of the reflected light beam from a point of the subject, it cannot measure the depth distribution of the whole subject.
Moreover, in the distance measuring method using the intensity modulation disclosed in xe2x80x9cDevelopment Axi-Vision Cameraxe2x80x9d by Kawakita et al. (3D Image Conference ""99, 1999), it is necessary to perform the light modulation at a very high speed in order to realize the intensity-modulation. Thus, a simple measurement cannot be realized. In addition, the measurement may include the time difference, thus preventing a precise measurement for the moving subject.
Therefore, it is an object of the present invention to provide an image capturing apparatus and a distance measuring method that overcome the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, an image capturing apparatus for obtaining information regarding a depth of a subject, comprises: an illumination unit operable to cast a first illumination light beam mainly containing a first wavelength and having a first intensity distribution on a plane perpendicular to an optical axis of the first illumination light beam and a second illumination light beam mainly containing a second wavelength and a third wavelength and having a second intensity distribution on a plane perpendicular to an optical axis of the second illumination light beam onto the subject, the second and third wavelengths being different from the first wavelength, the second intensity distribution being different from the first intensity distribution; and a depth calculation unit operable to calculate a depth-direction distance to the subject based on outgoing light beams from the subject.
The first illumination light beam may have an intensity that monotonously increases along a first direction on the plane perpendicular to the optical axis thereof, and the second illumination light beam may have an intensity that monotonously decreases along a second direction on the plane perpendicular to the optical axis thereof, the second direction being opposite to the first direction.
The first illumination light beam may have the first intensity distribution in which, with increase of a distance from the optical axis thereof on the plane perpendicular to the optical axis, an intensity monotonously increases or decreases, and the second illumination light may have the second intensity distribution in which, with increase of a distance from the optical axis thereof on the plane perpendicular to the optical axis, an intensity monotonously decreases when the first illumination light increases or increases when the first illumination light decreases.
The illumination unit may cast the first and second illumination light beams onto the subject simultaneously.
The image capturing apparatus may further comprise: an optically converging unit operable to converge the outgoing light beams from the subject onto which the first and second illumination light beams are cast; a separation unit operable to optically separate the outgoing light beams into a first outgoing light beam having the first wavelength, a second outgoing light beam having the second wavelength, and a third outgoing light beam having the third wavelength; a light-receiving unit operable to receive the first, second and third outgoing light beams after being are separated by the separation unit and converged by the optically converging unit; and a light intensity detector operable to detect intensities of the first, second and third outgoing light beams received by the light-receiving unit, wherein the depth calculation unit calculates the depth-direction distance to the subject by using the intensities of the first, second and third outgoing light beams.
The first illumination light beam may have an intensity that increases on the plane perpendicular to the optical axis thereof along a first direction parallel to a line obtained by projecting a line connecting the illumination unit to the light-receiving unit or the optical converging unit on the plane perpendicular to the optical axis thereof, and the second illumination light beam may have an intensity that increases on the plane perpendicular to the optical axis thereof along a second direction opposite to the first direction.
The illumination unit may include a first illumination optical filter operable to transmit light having the first wavelength and a second illumination optical filter operable to transmit light having the second and third wavelengths. In this case, the first and second illumination optical filters are arranged in such a manner that the first and second illumination light beams are incident on the first and second illumination optical filters, respectively.
The first illumination optical filter may have a transmittance that increases along a first direction on an incident surface thereof, while the second illumination optical filter have a transmittance that increases along a second direction on an incident surface thereof, the second direction being opposite to the first direction.
The first illumination optical filter may have a transmittance that increases or decreases with increase of a distance from the optical axis of the first illumination light beam on the incident surface thereof, while the second illumination optical filter has a transmittance that, with increase of a distance from the optical axis of the second illumination light beam on the incident surface, decreases in a case where the transmittance of the first illumination optical filter increases with the increase of the distance from the optical axis of the first illumination light beam or increases in a case where the transmittance of the first illumination optical filter decreases with the increase of the distance from the optical axis of the first illumination light beam.
The separation unit may include a first outgoing optical filter operable to transmit light having the first wavelength, a second outgoing optical filter operable to transmit light having the second wavelength, and a third outgoing optical filter operable to transmit light having the third wavelength. In this case, the first, second and third outgoing optical filters are arranged in such a manner that the first, second and third outgoing light beams are incident on the first, second and third outgoing optical filters, respectively.
The separation unit may include a first outgoing optical filter operable to transmit light having the first wavelength and a second outgoing optical filter operable to transmit light having the second and third wavelengths. In this case, the first and second outgoing optical filters are arranged in such a manner that the first outgoing light beam is incident on the first outgoing optical filter while the second and third outgoing light beams are incident on the second outgoing optical filter.
The light-receiving unit may include a solid state image sensor, and the separation unit may include a first outgoing optical filter that transmits light having the first wavelength, a second outgoing optical filter that transmits light having the second wavelength and a third outgoing optical filter that transmits light having the third wavelength, the first, second and third outgoing optical filters being arranged alternately on a light-receiving surface of the solid state image sensor.
The depth calculation unit may calculate the depth-direction distance to the subject by using a value based on the intensities of the second and third outgoing light beams and the intensity of the first outgoing light beam.
The depth calculation unit may calculate the depth-direction distance to the subject by using an averaged intensity of the intensities of the second and third outgoing light beams, and the intensity of the first outgoing light beam.
The second wavelength may be shorter than the first wavelength while the third wavelength is longer than the first wavelength. In this case, the image capturing apparatus may further comprise: an optically converging unit operable to converge the outgoing light beams from the subject onto which the first and second illumination light beams are cast; a separation unit operable to optically separate the outgoing light beams into a first outgoing light beam having the first wavelength and a second outgoing light beam having the second and third wavelengths; a light-receiving unit operable to receive the first and second outgoing light beams after being separated by the separation unit and converged by the optically converging unit; and a light intensity detector operable to detect intensities of the first and second outgoing light beams received by the light-receiving unit, wherein the depth calculation unit calculates the depth-direction distance to the subject by using the intensities of the first and second outgoing light beams.
The depth calculation unit may calculate the depth-direction distance to the subject by using the intensity of the first outgoing light beam and a half of the intensity of the second outgoing light beam.
The light intensity detector may calculate the intensities of the first and second outgoing light beams for each pixel of an image of the subject taken by the light-receiving unit. In this case, the depth calculation unit calculates a depth distribution of the subject by obtaining the depth-direction distance to a region of the subject corresponding to every pixel.
The first and second illumination light beams may be light beams in an infrared region, and the separation unit may further include a device operable to optically separate visible light from the outgoing light beams from the subject. In this case, the light-receiving unit may further include a solid state image sensor for visible light operable to receive the visible light that is optically separated by the separation unit and is converged by the optically converging unit, and the image capturing apparatus may further comprise a recording unit operable to record both the depth distribution of the subject calculated by the depth calculation unit and the image of the subject taken by the solid-state image sensor for visible light.
According to a second aspect of the present invention, a distance measuring method for obtaining information regarding a depth of a subject, comprises: an illumination step for simultaneously casting a first illumination light beam mainly containing a first wavelength and having a first intensity distribution on a plane perpendicular to an optical axis thereof and a second illumination light beam mainly containing a second wavelength and a third wavelength and having a second intensity distribution on a plane perpendicular to an optical axis thereof onto the subject, the second and third wavelengths being different from the first wavelength, the second intensity distribution being different from the first intensity distribution; a separation step for optically separating outgoing light beams from the subject onto which the first and second illumination light beams are cast into a first outgoing light beam having the first wavelength, a second outgoing light beam having the second wavelength, and a third outgoing light beam having the third wavelength; a capturing step for capturing the first, second and third outgoing light beams; a light intensity detection step for detecting the intensities of the captured first, second and third outgoing light beams; and a depth calculation step for calculating a depth-direction distance to the subject based on the intensities of the first, second and third outgoing light beams.
The depth-direction distance to the subject may be calculated based on a value based on the intensities of the second and third outgoing light beams and the intensity of the first outgoing light beam in the depth calculation step.
The depth-direction distance to the subject may be calculated based on an averaged intensity of the intensities of the second and third outgoing light beams and the intensity of the first outgoing light beam in the depth calculation step.
According to a third aspect of the present invention, a distance measuring method for obtaining information regarding a depth of a subject, comprises: an illumination step for simultaneously casting a first illumination light beam mainly containing a first wavelength and having a first intensity distribution on a plane perpendicular to an optical axis of the first illumination light beam and a second illumination light beam mainly containing a second wavelength and a third wavelength and having a second intensity distribution on a plane perpendicular to an optical axis of the second illumination light beam onto the subject, the second wavelength being shorter than the first wavelength, the third wavelength being longer than the first wavelength, the second intensity distribution being different from the first intensity distribution; a separation step for optically separating the outgoing light beams into a first outgoing light beam having the first wavelength and a second outgoing light beam having the second and third wavelengths; a capturing step for capturing the first and second outgoing light beams; a light intensity detection step for detecting the intensities of the first and second outgoing light beams; and a depth calculation step for calculating a depth-direction distance to the subject based on the intensities of the first and second outgoing light beams.
The depth-direction distance to the subject may be calculated based on the intensity of the first outgoing light beam and a half of the intensity of the second outgoing light beam in the depth calculation step.
According to a fourth aspect of the present invention, an image capturing apparatus for obtaining information regarding a depth of a subject, comprises: an illumination unit operable to cast a first illumination light beam mainly containing a first wavelength and a second illumination light beam mainly containing a second wavelength and a third wavelength, the first and second illumination light beams being modulated in such a manner that the intensities of the first and second illumination light beams are changed along the respective traveling directions, the second and third wavelengths being different from the first wavelength; and a depth calculation unit operable to calculate a depth-direction distance to the subject based on outgoing light beams from the subject onto which the first and second illumination light beams are cast.
The first illumination light beam may be modulated in such a manner that the intensity thereof monotonously increases or decreases along the traveling direction thereof, and the second illumination light beam may be modulated in such a manner that the intensity thereof monotonously decreases along the traveling direction of the second illumination light beam when the intensity of the first illumination light beam monotonously increases along the traveling direction of the first illumination light beam, or increases along the traveling direction of the second illumination light beam when the intensity of the first illumination light beam monotonously decreases along the traveling direction of the first illumination light beam.
The image capturing apparatus may further comprise a modulation unit operable to change the intensities of the first and second illumination light beams by temporal modulation.
The second wavelength may be shorter than the first wavelength while the third wavelength is longer than the first wavelength, and the image capturing apparatus may further comprise: an optically converging unit operable to converge the outgoing light beams from the subject onto which the first and second illumination light beams are cast; a separation unit operable to optically separate the outgoing light beams into a first outgoing light beam having the first wavelength and a second outgoing light beam having the second and third wavelengths; a light-receiving unit operable to receive the first and second outgoing light beams after being separated by the separation unit and converged by the optically converging unit; and a light intensity detector operable to detect intensities of the first and second outgoing light beams received by the light-receiving unit, wherein the depth calculation unit calculates the depth-direction distance to the subject by using the intensities of the first and second outgoing light beams.
According to a fifth aspect of the present invention, a distance measuring method for obtaining information regarding a depth of a subject, comprises: an illumination step for simultaneously casting a first illumination light beam mainly containing a first wavelength and a second illumination light beam mainly containing a second wavelength and a third wavelength, the first and second illumination light beams being modulated in such a manner that the intensities of the first and second illumination light beams are changed along traveling directions thereof, respectively; a separation step for optically separating the outgoing light beams from the subject into a first outgoing light beam having the first wavelength, a second outgoing light beam having the second wavelength, and a third outgoing light beam having the third wavelength; a capturing step for capturing the first, second and third outgoing light beams; a light intensity detection step for detecting the intensities of the first, second and third outgoing light beams; and a depth calculation step for calculating a depth-direction distance to the subject based on the intensities of the first, second and third outgoing light beams.
The depth-direction distance to the subject may be calculated based on the intensity of the first outgoing light beam and a value based on the intensities of the second and third outgoing light beams in the depth calculation step.
According to a sixth aspect of the present invention, a distance measuring method for obtaining information regarding a depth of a subject, comprises: an illumination step for simultaneously casting a first illumination light beam mainly containing a first wavelength and a second illumination light beam mainly containing a second wavelength and a third wavelength, the first and second illumination light beams being modulated in such a manner that the intensities of the first and second illumination light beams are changed along traveling directions thereof, respectively, the second wavelength being shorter than the first wavelength, the third wavelength being longer than the first wavelength; a separation step for optically separating the outgoing light beams into a first outgoing light beam having the first wavelength and a second outgoing light beam having the second and third wavelengths; a capturing step for capturing the first and second outgoing light beams; a light intensity detection step for detecting the intensities of the first and second outgoing light beams; and a depth calculation step for calculating a depth-direction distance to the subject based on the intensities of the first and second outgoing light beams.
This summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the above described features. The above and other features and advantages of the present invention will become more apparent from the following description of embodiments taken in conjunction with the accompanying drawings.